Search for γ -ray E mission from Radio-Quiet Seyfert AGN

1. Search for γ-ray Emission from Radio-Quiet SeyfertAGN Masaaki Hayashida (KIPAC/SLAC and Kyoto Univ.) <mahaya@slac.stanford.edu>, Keith Bechtol (SLAC/KIPAC), Lukasz Stawarz (ISAS/JAXA),and Greg Madejski (KIPAC/SLAC) on behalf of the Fermi Large Area Telescope Collaboration Abstract In contrast to radio galaxies with luminous relativistic jets, radio emission from Seyferts is generally weak, usually dominated by diffuse emission of the interstellar medium. Low-power radio-emitting outflows have been resolved in some Seyferts, but little is known about their γ-ray properties. We report results from a systematic investigation of Seyfert AGN at MeV-GeV photon energies, utilizing two years of Fermi-LAT data, and a uniform sample of objects selected from the Swift-BAT 58-month catalog. Our preliminary results indicate that radio-quiet Seyfertsare `γ-ray quiet' as a class of AGN. The derived upper limits in the MeV-GeV range exclude g-rayemission from Seyfertnuclei exceeding 1% of their X-ray luminosities. SeyfertGalaxies Recent discoveries of γ-ray emission from non-blazar AGN by Fermi-LAT raise the question:Are there galaxies capable of producing strong g-ray emission without luminous relativistic jets and/or starburst activity? Obvious candidates might be AGNs generally devoid of prominent jets, e.g. Seyfert galaxies, identified in the optical regime as AGN hosted by late-type galaxies with bright unresolved nuclei. Seyfertsare also bright in X-rays, and both the optical and the X-ray emission components are produced by matter accreting onto supermassiveblack holes. Hard X-ray observations are used to select a complete and unbiased sample of Seyfert galaxies because hard X-ray emission is a clear and common signature of AGN activity. The galaxies are selected on a basis of the Swift-BAT 58 month catalog [2]. In order to extract `radio-quiet’ objects, we defined `hard X-ray radio loudness’ as follows: The 1.4 GHz radio fluxes are gathered from catalogs such as NVSS, FIRST and PKSCAT90. • Summary of Selection Criteria (120 total objects in sample) • Hard X-ray fluxes [nFn]14-195 keV > 2.5x10-11[erg/cm2/s] in Swift-BAT catalog • Spectral classification as `galaxies' or `Seyfert galaxies' in Swift-BAT catalog • Hard X-ray radio loudness parameter Rrx < 10-4 (selects radio-quiet objects) • - This happens to exclude two Seyferts with high star-forming rate, NGC 1068 and NGC 4945 • Galactic coordinates |b| > 20o for -20o< l < 20o, and |b| > 10o otherwise • ( Sample Selection selected Figure 2. Distribution of ‘hard X-ray radio loudness’ parameter for Seyfert galaxies (both radio-quiet and radio-loud, yellow), and comparison sample of beamed AGN (known as radio-loud, blue). Figure 1. Schematic diagram of optical to X-ray emission ingredients in radio-quiet AGN powered by accretion onto supermassive back holes. Taken from [1]. • Analysis Parameters • Observation times: August 4, 2008 - August 4, 2010 • IRF: P6_V11_DIFFUSE • Photon events: 0.2-100 GeV, `diffuse’ class • Source fitting model: power law -> dF/dE = N(E/E0)-G LAT Data Analysis and Results • Results • No significant excess is found positionally coincident with any Seyfert galaxies in the sample • 95 % upper limits (UL) calculated with a fixed photon index G=2.5 in a range of 0.1-10 GeV are presented • Mean value of the UL: ~ 5x10-9ph cm-2 s-1 • Comparison with EGRET Results • (0.5 –1.5)x10-7ph cm-2 s-1(individual sources) [3] • (0.3 –1.5)x10-8ph cm-2s-1 (stacking with brighest 32 Seyferts)[4] Figure3. Histogram of g-ray photon flux upper limits (95 % C.L.) for the analyzed Seyfert galaxies. • Implications ong-ray emission models from Seyfert galaxies based on our results of g-ray upper limits : • Any jet-related g-ray emission components in radio-quiet AGNs, if present, is not prominent. • Gammarays from Seyfertscould originate from a disk coronae involving a non-thermal electron population [e.g., 6, 7]. However, the non-thermal power-law tails in the MeV range should not constitute more than ~ 10 % of total energy radiation in the X-ray regime. • GeV photons from Seyferts could also be generated through proton-proton interactions in the innermost parts of accretion disks [e.g., 8].In the case of a maximally spinning black hole, some models predict that hadronic emission in the 0.1-10 GeV range could reach > 10 % of the disk/disk corona X-ray luminosity, but we did find any such signal in our analysis. Discussion of Emission Models Multi-wavelength Comparison We compare hard X-ray (14-195 keV) emission measured with Swift-BAT to derived ULs for γ-ray energy flux and luminosity. GeV emission from Seyferts is excluded to the level of Lg/LX < 0.1 for most sources, and < 0.01 for several sources. Since hard X-ray luminosity is expected to constitute about 10% of the bolometric AGN-related luminosity, LAGN, of a typical Seyfertgalaxy [5], the GeV emission probed in our analysis reaches Lg/LAGN < 0.001 in several examples. . Figure 4. Hard X-ray (14-195keV) versus UL for the γ-ray (0.1-10 MeV) for the analyzed sample of Seyferts. Dotted lines denote the ratios between g-ray and hard X-ray emission of 1, 0.1, and 0.01, respectively. Left: energy flux. Right: luminosity. All points represent g-ray upper limits • Radio-quiet Seyfert galaxies are generally g-ray quiet as a class of AGNs (0.2-100 GeV) • Upper limits in the MeV-GeV domain exclude the presence of g-rayemission in Seyfert nuclei exceeding 1% of the X-ray luminosities • MeV-GeV emission detected so far by Fermi-LAT from a few radio-quiet Seyfert galaxies (NGC 1068, NGC 4945, both well-known starburst galaxies) may be attributed to cosmic-ray induced emission in the interstellar medium of host galaxies Conclusions References [1] Mushotzky et al. 1993, ARA&A, 31, 717 [2] http://heasarc.gsfc.nasa.gov/docs/swift/results/bs58mon/ [3] Linet al.1993, ApJL, 416, L53 [4] Cilliset al. 2004, ApJ, 601, 142 [5] Ho 2008, ARA&A, 46, 475 [6]Zdziarski & Lightman1985, ApJL, 294, L79 [7] Inoue, Totani & Ueda 2008, ApJL, 672, L5 [8] Niedzwiecki, Xie & Zdziarski 2009, The Extreme Sky: Sampling the Universe above 10 keV